1. Technical Field
The present invention relates to a physical quantity sensor and an electronic apparatus.
2. Related Art
In recent years, techniques for realizing a physical quantity sensor that is small and has high sensitivity have been developed using, for example, a silicon MEMS (Micro Electro Mechanical Systems) technique.
For example, JP-T-2009-537803 (Patent Document 1) discloses an acceleration sensor with a mass having two wings rotatable about a torsion web. The acceleration sensor is configured such that through-holes are disposed in each of the two wings and thus torsions of the same magnitude in opposite directions relative to the torsion web cause damping torques of the same magnitude. Moreover, the acceleration sensor has a first electrode below one of the wings and a second electrode below the other wing. The acceleration sensor detects acceleration based on an electrostatic capacitance between the one wing and the first electrode and an electrostatic capacitance between the other wing and the second electrode.
In the acceleration sensor of Patent Document 1, the mass is accommodated in a casing filled with a gas such as nitrogen. By disposing the through-holes in the wing, damping (action to stop the movement of the mass, or flow resistance) caused by the viscosity of the gas can be reduced. With this configuration, the detection sensitivity can be enhanced.
However, in the acceleration sensor of Patent Document 1, since the size of the through-hole is different between the two wings, the area of a region where the one wing overlaps with the first electrode in plan view is different from the area of a region where the other wing overlaps with the second electrode in plan view. Therefore, in an initial state (state where acceleration is not applied, or state where the wings are horizontal), the electrostatic capacitance between the one wing and the first electrode is different from the electrostatic capacitance between the other wing and the second electrode. Hence, for eliminating the difference between the initial capacitances, an adjustment of a gap between the wing and the electrode, or a circuit or the like for correcting the difference between the initial capacitances is required. Therefore, the configuration of an apparatus cannot be simplified, leading to problems such as increases in manufacturing processes and cost.